Acoustic apparatus



epit. 12, 1939. G. M. GIANNINI ACOUSTIC APPARATUS Filed Jan. 10, 1938 2Sheets-Sheet 1 RI m m MN m WA flm 1m M W L W m% &pfr. E2, 3939.

G. M. GKANNINI ACOUSTIC APPARATUS 2 Sheets-Sheet 2 Filed Jan. 10, 1938INVENTOR @BRZELM GMNNIN] /f;/%fi7f ATTORNEY.

rei nied Sept. 12, 1939 4 p I 2,172,871

UNllED STATES PATENT OFFICE ACOUSTIC APPARATUS Gabriel Maria Giannini,Great Neck, N. Y., assigner to Automatic Electric Company, Chicago,111., a corporation of Delaware Application January 10, 1938, Serial No.184,285 Claims. (01.181-26) My invention relates to acoustic devices fordesound generator and the receiving device and the termining thedirection of propagation of sound angle which the receiving device makeswith this waves, and to locatingand distance-measuring line whenadjusted to give a minimum response,

systems using such devices. and can be read directly from aproperly-cali- 5 As my inventiton is particularly applicable for bratedscale. 5 use in aviation, I shall describe the same in this In orderthat the invention may be clearly connection. However, it is not limitedthereto but understood and readily carried into effect, I shall isequally applicable for use in any detecting or describe the same in moredetail with reference measuring system in which it is desired to accutothe accompanying drawings, in which:

l0 rately and readily determine the direction of Figure 1 is asectionized side-view of a receiving propagation of a sound wave, forinstance in device according to the invention; marine navigation. Fig. 2is a section through line 2-2 of Fig. 1; The main object of my inventionisto provide Fig. 3 is a perspective view of a receiving device a soundtranslating device which isvery sensiaccording to another embodiment ofthe inven- 1 tive to sound waves of a given frequency and tion; has veryhigh directional characteristics. Fig. 4 is a diagram illustrating theoperation of Another object of my invention is to provide an the deviceshown in Figs. 1 and 2; acoustic system for accurately and readily de-Fig. 4a is a graph showing the directional termining the position of anairplane from a characteristics of the device shown in Figure 3; pointon the ground, or vice versa. Fig. ii is a diagram illustrating anapparatus 20 A further object of my invention is to provide a and methodfor determining the distance of an simple acoustic altimeter foraccurately and airplane from the ground; quickly determining thedistance of a plane from Fig. 6 is a diagram illustrating a system for pthe ground when landing or during low flying. landing a plane with thesound-receiving device Further objects of my invention will appear ofFigs. 1 to 3, 25 as the description progresses. Fig. 7 is a sectionalview on an enlarged scale The device according to the invention, whosealong line of Figure 3, and operation is based on the interference ofsound Fig. 8 is a sectional view on an enlarged scale waves, comprises aplurality of tubular impedance along line 8-8 of Figure 5. elements oneof which difi'ers in acoustic wave The planar receiver illustrated inFigs. 1 and 2 30 length from the others by one-half, or onecomprises twoimpedance elements A and B and half plus an integer, of the wave-lengthof the a microphone unit 0, which is of the moving sound to be detected,coupled to a sound-transcoil type, and comprises a cup-shaped permanentlating device, such as a microphone. When these magnet I carrying a core2 of soft iron. Supelements are so arranged that their receiving portedfrom its edge by magnet I is a conical 35 ends lie parallel to a wavefront, the sound transdiaphragm 3 which carries at its vertex a coil 4mitted through difierent impedance elements will having lea-d8 A ring 6of Soft iron pported reach the sound-translating device 180 out of by man l serves to complete the n ic phase, and the resulting sound will benil or mincircuit and form an intense magnetic field in the 0 mum;whereas only a slight displacement from vicinity of coil 5. By 'a planarreceiver is 40 this position will produce a relatively high remeant onethat is responsive in a single plane or sponse. line. It should be notedthat it is unnecessary The present invention also includes a method touse a microphoneof the type shown, although and apparatus by which anaviator can rapidly such a microphone gives very good results.

15 determine his distance from the ground when A ring I of non-mag eticmaterial secures landing. For this purpose I propagate toward the cone 3to magnet I, and also forms a n atching ground, sound waves of apredetermined and sub chamber l0. Secured to ring i, for instance bystantially monochromatic frequency from a genmeans of a suitable wax H,are two impedance erator located at one point on the plane, anddeelements A and B.

termine the direction of the sound waves re- As shown, impedance elementA consists of fiected from the ground, by means of the receivnineteenmetal tubes 8, for instance of copper ing device according to theinvention, which is or pl rial of q l len h and havin located at anotherpoint on the plane, The disan inside diameter of about whereas imtanceof the plane from the ground can be readily pedance element B consistsof nineteen tubes 9,

ascertained from the known distance between the which also are of equallength. In accordance 55 be equal to e.

with the invention tubes 8 difier in length from tubes 9 by /2, or by aninteger plus /2, of the I wave-length of the sound whose direction is tobe determined. More particularly, if tubes 9 have a length equal to onewave-length of the sound to be recorded, tubes 8 may have a lengthinwhich the ends of tubes 8 and lie in alternate vertical rows. Such aconstruction is somewhat difficult to illustrate in a clear manner, butit can be readily produced by cutting all the tubes of each group of thesame length, securing them at one end to the ring I, and then bendingthe tubes 8 so their free ends lie in a plane as shown.

In the present instance the receiver is designed to detect the wavefronts of sound waves having a frequency of about 2,000 vibrations persecond. In order to keep the dimensions of the receiver as small aspossible, the tubes 0 were given a length of about 12 inches, and tubes3 were given a length of about 12"+ /2 12+3=15".

The receiver illustrated in Fig. 3, which can be considered as atwo-dimensional receiver, is the same as that shown in Fig. 1 exceptthat it has a third impedance element D which is the same as element Aexcept that it is displaced ninety degrees, 1. e., the open ends ofelements A, B, and D lie in a plane and substantially at the' verticesof a right angle isosceles triangle. In this case also the tubes are soarranged that their ends are evenly distributed over the diaphragm ofthe transmitter. This is shown in Figure 7 in which the tubes of elementA are indicated by crosses, the tubes of element D are indicated bydots, and the remaining tubes are those of element B. By atwo-dimensional receiver is meant one that is responsive in twodimensions. More particularly if a planar receiver were used to detectthe location of an airplane from which sound is propagated it would bepossible to locate the plane accurately only in a plane. However, with atwo-dimensional receiver it would be possible to locate the airplane ina line.

' The directional characteristics of a receiver according to theinvention is illustrated in Figures 4 and 4a in which reference numeralI I indicates a sound-wave having a direction D and a substantiallymonochromatic frequency of, fr instance, 2000 vibrations per second:10%, and reference numeral I2 indicates a receiver such as shown inFig. 1 having an axis I3.

In the polar graph of Figure 4a the radius vectors indicate theintensity of sound received by receiver I2 when it is arranged with itsaxis lying in the direction of the vector. For example, when receiver I2is in the position shown, i. e., with its axis I3 parallel to thedirection of propagation D of wave I I, the intensity of the soundreceived will When the receiver is rotated 2 degrees from thisposition,.i. e., 0=87 /2%, the sound intensity increases to a valueindicated by j, which is about five times as great as e. Thus, it isseen that the receiver according to the invention is very directional,i. e., when it is rotated through an angle of only 2 degrees there is achange in intensity of about 80%, which makes it possible to locate thedirection of propagation of a wave front with great accuracy. Thisaccuracy may be varied by varying the distance between the ends of theimpedance elements-the more apart the openings are the greater theaccuracy will be.

While Fig. 4a. illustrates the characteristics of a receiver of the typeillustrated in Fig. 1, the same results, but in two dimensions, areobtained with the receiver of Fig. 3.

Because of these extremely good directional characteristics, receiversof the type according to the invention have a very wide range ofapplications, especially in aviation and in marine navigation. Asstated, my invention also includes a method and apparatus fordetermining the distance that a plane is from the ground when landing orflying low, by using the receiver according to the invention.

Such an apparatus and method is illustrated in Fig. 5 in which areceiver I2, such as illustrated in Fig. l-, is supported on the tail ofthe fuselage of a plane and a sound generator I4 is located at the frontof the plane. Generator I4 is of the type which generates sound waves ofa substantially mnonchromatic frequency, and as such generators ,arewell known in the art, further description or illustration of the sameare believed to be unnecessary. The manner in which the receiver I2 ismounted on the plane is more clearly shown in Figure 8. In this figurethe reference numeral 2| indicates the fuselage of the plane. Thereceiver I2 is mounted on a pivot 22 which is rotatably mounted on thefuselage 2| so that the receiver can be rotated in a plane perpendicularto the plane of the drawings.

Generator I4 propagates toward the ground, sound waves indicated byreference numeral I5, which are reflected-toward the plane as soundwaves I6. Receiver I2 is then rotated in the plane of the drawings untilthere is a minimum response, and the distance from the ground can becomputed from the angle which the axis of the receiver makes with theline between the generator and receiver, and the distance between thereceiver and generator, or can be read directly from a properlycalibrated scale.

Such a method of determining the distance is very accurate, and becomesmore so as the plane approaches the ground, particularly when the planeis less than 10 plane lengths from the ground. This makes the methodparticularly useful in landing an airplane, because when landing it isvery important that the aviator'knows when the plane is about 10 feetabove the ground in order that he may level off and effect a threepointlanding.

I am well aware of the fact that sound-wave altimeters have beenproposed for determining the distance of aircraft from the ground.However, such altimeters have been based on measuring the time intervalrequired for a sound generated on an aircraft to be reflected from theearth and returned to the aircraft. Such systems, however, arerelatively complicated and have a low degree of accuracy when the planeis relatively near the ground. On the contrary, my apparatus becomesmore accurate as the distance between the plane and the ground becomesless, which as stated makes it particularly adapted for landing a plane.

Figure 6 illustrates a method of landing a plane by means of adirectional receiver according to the invention. As shown, a soundgenerator I! located on the ground propagates toward the 2,172,871substantially monochromatic frequency. Located on the plane is areceiver IQ of the type illustrated in Fig. 3, by means of which theaviator may readily and accurately detect the direction of the soundwaves and effect a proper landing.

The expression an integer plus the wave length as used in the claims isto be understood to include the wave length, i. e., assuming zero to bean integer.

While I have described my invention in connection with specific examplesand with reference to particular applications, I do not wish to belimited thereto, but desire the appended claims to be construed asbroadly as permissible in view of the prior art.

What I claim is:

1. A device for determining the direction of the Wave front of a soundof predetermined and substantially monochromatic frequency comprising asound-translating device, and a plurality of hollow impedance membershaving one end connected to said sound-translating device and theirother ends spaced apart in a common plane, one of said members differingin acoustic wave length from the remaining members by an integer plusthe wave-length of the sound to be received.

2. A device for determining the direction of the wave front of a soundof predetermined and substantially monochromatic frequency comprising asound-translating device, and two groups of impedance members connectedbetween said sound-translating device and the sound to be received withtheir receiving ends spaced apart in a common plane, the members of eachgroup being of substantially equal lengthand the members of one groupdifiering in "acoustic wave-length from the members of the other groupby an integer plus the wave-length of the sound to be received.

3. A device for determining the direction of the wave front of a soundof predetermined and substantially monochromatic frequency comprising asound-translating device having a diaphragm, and a plurality ofimpedance elements connected between said sound-translating device andthe sound to be received with their receiving ends spaced apart in acommon plane and with their other ends distributed substantiallyuniformly with respect to said diaphragm, each of said elementscomprising a plurality of tubular members of the same length, themembers of one of said elements differing in acoustic wave-length fromthe other members by an integer plus of the wave-length of the sound tobe received.

4. A device for determining the direction of the wave front of a soundof predetermined and substantially monochromatic frequency comprising asound-translaitng device, and three groups of tubular impedance membershaving one end connected to said receiver and their other ends spacedapart in a common plane substantially at the vertices of a right angleisosceles triangle, the members of one 'of said groups differing inacoustic wave-length from the members of the other two groups by aninteger plus the wavelength of the sound to be received.

5. In combination a generator for propagating sound waves of asubstantially monochromatic frequency, and a device for determining thedirection of the wave front of said sound waves comprising asound-translating device, and two tubular impedance elements lraving oneof their ends lying in a common plane and their other ends connected tosaid sound-translating device, one of said elements differing in acusticwave length from the other element by an integer plus ,the wave lengthof said sound waves.

GABRIEL MARIA GIANNINI.

